Cerium-Enhanced Stability of a High-Entropy Alloy Catalyst for the Oxygen Reduction Reaction in Acidic Media

Abstract

Low-platinum high-entropy alloys (HEAs) have emerged as a highly promising alternative to commercial Pt/C for the oxygen reduction reaction (ORR). However, they suffer from transition metal leaching and structural degradation, particularly under the harsh acidic conditions of proton-exchange membrane fuel cell (PEMFC) operation. Herein, we propose an effective endogenous-alloying strategy, which involves incorporating cerium (Ce) as an endogenous alloying element into the HEA lattice, rather than as a discrete physical additive. This approach leverages the dynamic Ce3+/Ce4+ redox couple to effectively scavenge free radicals at the atomic level, fundamentally enhancing durability from within. The resultant low-platinum quinary catalyst Pt0.7Ce0.3FeCoNi (PCFCN) exhibits a disruptive "negative degradation" phenomenon in acidic media. After 30,000 accelerated durability test cycles, its mass activity not only showed no decay but also remarkably increased from 0.72 to 2.18 A mg(Pt)(-1), representing a 203% enhancement, far surpassing those of the control catalysts and state-of-the-art catalysts. This study not only reports a superior catalyst but also establishes a material paradigm for designing ultrastable high-entropy alloy electrocatalysts through endogenous rare-earth alloying.